helium -
a very light colorless element that is one of the six inert gasses; the most difficult gas to liquefy; occurs in economically extractable amounts in certain natural gases (as those found in Texas and Kansas)
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table. Its boiling and melting points are the lowest among the elements and it exists only as a gas except in extreme conditions.
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helium A colorless, odorless, tasteless, nearly inert noble gas with the symbol He and atomic number 2. It is after hydrogen the second most abundant element in the universe. It is a component of air and is being used for balloon and airship fillings, as well as for deep-sea breathing systems in combination with oxygen.